It is well-known that there are various diagnoses for which it is needed or desired to hold bones within a human or animal body in a fixed position with respect to each other. One such diagnosis for which it is desired to hold bones within a human or animal body in a fixed position with respect to each other is an accidental or intentional fracture of a bone. Another such diagnosis for which it is desired to hold bones within a human or animal body in a fixed position with respect to each other is in a surgical fusion procedure (e.g., a sacroiliac fusion).
Irrespective of the diagnosis leading to the need or desire to hold bones within a human or animal body in a fixed position with respect to each other, one or more bone screws are well-known to be used for such purpose. The bone screws, which are often used in combination with other fastening implements (e.g., bone plates) can be threadedly inserted into the two or more separate bone pieces (e.g., two or more different bones and/or segments of a given bone) for securing such two or more separate bone pieces in fixed relationship with respect to each other. The bone screw(s) thereby hold(s) the bone pieces in a stationary position with respect to each other and, in some usages, thereby allows bone material to grow therebetween to fuse the bone pieces together. Such bone growth supplements the strength provided by the bone screw to prevent the bones pieces from moving with respect to each other.
A specific application for bone screws is sacroiliac joint fusion. As shown in FIG. 1, the sacroiliac (SI) joint 10 is located in the human body between the sacrum 11 and the hip bones 12, known as the ilium. The sacroiliac joint functions to transmit forces from the spine 14, including vertebrae 14a, intervertebral discs 14b and the coccyx 14c, to the lower extremities. The sacroiliac joint 10 is supported by ligaments and muscle. The sacroiliac joint 10 can degenerate over time, requiring a fusion procedure to stabilize the degenerated segment. For example, one condition, degenerative sacroiliitis, results in a narrow joint space with bone spur formation. Iatrogenic (i.e., induced by treatment) procedures, such as iliac bone graft damaging ligaments of the joint and/or previous fusions, can also cause degeneration, requiring sacroiliac joint fusion. Alternatively, infection, ligamentous disruption due to pregnancy, and/or trauma causing fracture dislocation may require a sacroiliac joint fusion procedure to provide sufficient stabilization to allow the patient to achieve a normal lifestyle.
Therefore, a bone screw for securing bones within a human or animal body in a fixed position with respect to each other and that does not inhibit growth of bone material between such bone pieces is advantageous, desirable and useful.